This invention relates to digital computer network technology. More specifically, it relates to methods and apparatus for implementing a new addressing scheme for nodes of an access network.
Broadband access technologies such as cable, fiber optic, and wireless have made rapid progress in recent years. Recently there has been a convergence of voice and data networks which is due in part to US deregulation of the telecommunications industry. In order to stay competitive, companies offering broadband access technologies need to support voice, video, and other high-bandwidth applications over their local access networks. For networks that use a shared access medium to communicate between subscribers and the service provider (e.g., cable networks, wireless networks, etc.), providing reliable high-quality voice/video communication over such networks is not an easy task.
One type of broadband access technology relates to cable modem networks. A cable modem network or “cable plant” employs cable modems, which are an improvement of conventional PC data modems and provide high speed connectivity. Cable modems are therefore instrumental in transforming the cable system into a full service provider of video, voice and data telecommunications services.
FIG. 1 shows a block diagram of a conventional two-way hybrid fiber-coaxial (HFC) cable network 100. As shown in FIG. 1, the cable network 100 includes a Head End complex 102 typically configured to service about 40,000 homes. The Head End complex 102 may include a plurality of components and/or systems (not shown) such as, for example, a Head End, a super Head End, a hub, a primary hub, a second hub, etc. Additionally, as shown in FIG. 1, the Head End complex 102 typically includes a Cable Modem Termination System (CMTS). Primary functions of the CMTS include (1) receiving data inputs from external sources 100 and converting the data for transmission over the cable plant; (2) providing appropriate Media Access Control (MAC) level packet headers for data received by the cable system, and (3) modulating and demodulating the data to and from the cable network. Typically, the Head End complex 102 is configured to provide a communication interface between nodes (e.g. cable modems) in the cable network and external networks such as, for example, the Internet. The cable modems typically reside at the subscriber premises 110A-D.
The Head End Complex 102 is typically connected to one or more fiber nodes 106 in the cable network. Each fiber node is, in turn, configured to service one or more subscriber groups 110. Each subscriber group typically comprises about 500 to 2000 households. A primary function of the fiber nodes 106 is to provide an optical-electronic signal interface between the Head End Complex 102 and the plurality of cable modems residing at the plurality of subscriber groups 110.
In order for data to be able to be transmitted effectively over a wide area network such as HFC or other broadband computer networks, a common standard for data transmission is typically adopted by network providers. A commonly used and well known standard for transmission of data or other information over HFC networks is the Data Over Cable System Interface Specification (DOCSIS). The DOCSIS standard has been publicly presented by Cable Television Laboratories, Inc. (Louisville, Colo.), in a document entitled, DOCSIS 1.1 RF Interface Specification (document control number SP-RFIv1.1-I06-001215, Dec. 15, 2000). That document is incorporated herein by reference for all purposes.
Communication between the Head End Complex 102 and fiber node 106a is typically implemented using modulated optical signals which travel over fiber optic cables. More specifically, during the transmission of modulated optical signals, multiple optical frequencies are modulated with data and transmitted over optical fibers such as, for example, optical fiber links 105a and 105b of FIG. 1, which are typically referred to as “RF fibers”. As shown in FIG. 1, the modulated optical signals transmitted from the Head End Complex 102 eventually terminate at the fiber node 106a. The fiber nodes maintain the signal modulation while converting from the fiber media to the coax media and back.
Each of the fiber nodes 106 is connected by a coaxial cable 107 to a respective group of cable modems residing at subscriber premises 10A-D. According to the DOCSIS standard, specific frequency ranges are used for transmitting downstream information from the CMTS to the cable modems, and other specific frequency ranges are used for transmitting upstream information from the cable modems to the CMTS.
Typically, digital data on upstream and downstream channels of the cable network is carried over radio frequency (“RF”) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission and convert downstream RF signal to digital form. The conversion is done at a subscriber's facility. At a Cable Modem Termination System (“CMTS”), located at a Head End Complex of the cable network, the conversions are reversed. The CMTS converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines to the subscriber premises. The cable modem then demodulates the RF signal and feeds the digital data to a computer. On the return path, the digital data is fed to the cable modem (from an associated PC for example), which converts it to a modulated RF signal. Once the CMTS receives the upstream RF signal, it demodulates it and transmits the digital data to an external source.
Data Communication in Cable Networks
In conventional DOCSIS systems, the CMTS may include a plurality of physically distinct line cards having appropriate hardware for communicating with cable modems in the network. Due to physical constraints, the upstream and downstream channels physically associated with a particular Line Card are typically grouped together and defined as one or more separate DOCSIS domains. Typically, each line card is pre-configured or pre-packaged to include the necessary hardware to enable that line card to provide a fixed number of upstream and/or downstream channels. For example, a typical line card configuration will include a single downstream transmitter (for the downstream channel) and one or more upstream receivers (for the upstream channels). The downstream channel is used by the CMTS to broadcast data to all cable modems (CMs) within that particular domain. Only the CMTS may transmit data on the downstream.
In order to allow the cable modems of a particular DOCSIS domain to transmit data to the CMTS, the cable modems share one or more upstream channels within that domain. Access to the upstream channel is controlled using a time division multiplexing (TDM) approach. Such an implementation requires that the CMTS and all cable modems sharing an upstream channel within a particular domain have a common concept of time so that when the CMTS tells a particular cable modem to transmit data at time T, the cable modem understands what to do. “Time” in this context may be tracked using a counter, commonly referred to as a timestamp counter, which, according to conventional implementations is a 32-bit counter that increments by one every clock pulse.
Because each line card is pre-configured to include a fixed number of upstream and/or downstream channels, the upstream and downstream channels of conventional HFC networks are conventionally grouped together based upon their physical associations. Thus, for example, if a conventional line card has been pre-configured to include one downstream channel and four upstream channels, a conventional DOCSIS-enabled HFC network will typically define a single DOCSIS domain as corresponding to the one downstream and four upstream channels which are physically associated with the 1×4 line card. Cable modems belonging to this DOCSIS domain are constrained to use only the upstream and downstream channels associated with this DOCSIS domain, and are therefore bandwidth limited. Moreover, it will be appreciated that each line card has a fixed amount of resources based on its particular hardware configuration. Because of this, it is not possible to add additional upstream or downstream channels to an existing line card residing within the CMTS without physically modifying the hardware configuration of that line card.
In conventional DOCSIS-enabled HFC networks, a defined DOCSIS domain will typically not include upstream and/or downstream channels from different line cards. One reason why conventional DOCSIS domains are defined so as not to include upstream and/or downstream channels from different line cards is that, typically, each line card includes a single MAC controller for scheduling timeslot allocations for the upstream channels associated with that line card. Moreover, it is typically the case in conventional DOCSIS implementations that the different MAC controllers residing on the different line cards are not synchronized with each other. As a result, upstream/downstream channels from different line cards are typically not grouped together in a DOCSIS domain since the upstream/downstream channels from different line cards will not be synchronized with each other. These issues are described in greater detail with respect to FIG. 2 of the drawings.
FIG. 2 shows a block diagram of a conventional configuration for an HFC network. As shown in FIG. 2, the CMTS 210 may include a plurality of physically distinct line cards, e.g. Line Card A 203 and Line Card B 204. Each line card provides a separate interface for communicating with a specific group of cable modems in the network. For example, Line Card A 203 includes a distinct group of ports (e.g., 205, 212) for communicating with cable modem Group A 260a, and Line Card B includes a separate distinct group of ports (e.g., 225, 233) for communicating with cable modem Group B 260b. 
Each line card within CMTS 210 includes a separate MAC controller for controlling the group of ports which reside on that physical line card. For example, on Line Card A, MAC controller 206 controls downstream transmitter 212 and the plurality of upstream receivers 205. Similarly, the MAC controller 208 on Line Card B controls downstream transmitter 233 and the plurality of upstream receivers 225.
According to conventional techniques, each MAC controller includes its own unique timestamp counter for generating a local time reference specific to the particular line card on which it resides. Thus, for example, MAC controller 206 includes a first timestamp counter (not shown) which generates a local time reference to be used by Line Card A for communicating with the plurality of Group A cable modems. Likewise, MAC controller 208 includes its own timestamp counter (not shown) for generating a local time reference to be used by Line Card B for communicating with the Group B cable modems. Typically, in conventional CMTS systems, the timestamp counters which reside on different line cards are not synchronized.
Because data-over-cable service is a relatively new and emerging technology, conventional cable networks have been designed to be efficient in handling burst data transmissions from the plurality of network cable modems to the CMTS. Additionally, conventional cable network configurations are designed to take into account the asymmetrical bandwidth allocation on the upstream and downstream channels. For example, a downstream channel will typically have a bandwidth of 30-50 Mbps, and an upstream channel will typically have a bandwidth of 1-10 Mbps. In taking the above factors into account, it is common practice to statically configure each line card to include a single downstream channel transmitter and a pre-determined number of upstream channel receivers.
As commonly known to one having ordinary skill in the art, the addressing scheme which is implemented in conventional HFC networks is unique for each DOCSIS domain. That is to say, each DOCSIS domain includes a pre-determined range of Service Identifier addresses or SIDs which are unique to that particular domain. According to the DOCSIS specification, SIDs are used to identify flows associated with particular cable modem in a particular DOCSIS domain. SIDs are also used by the CMTS to schedule upstream channel timeslot allocations for particular cable modems. Each SID is typically configured as a 14-bit binary number. Each cable modem typically has a primary SID and may also have one or more multiple secondary SIDs assigned to it for handling different types of service flows (e.g. data, VoIP, Video, etc).
Conventional DOCSIS addressing techniques typically allocate about 8000 SIDs for each DOCSIS domain. Moreover, each DOCSIS domain is limited to a fixed size due to the physical constraints described above. Consequently, the conventional DOCSIS protocol is not designed to take advantage of new and emerging broadband network applications such as video-on-demand, telephony, etc. Accordingly, there exists a continual need to improve access network configurations in order to accommodate new and emerging network applications and technologies.